Pandora

The Pandora is a demonic briefcase which appears in Devil May Cry 4, and is obtained after defeating Dagon in Mission 15. It can transform into 666 separate evil forms, and as you use its basic forms, the Disaster Gauge fills up. Once it is full, Dante can activate his Gunslinger Style to use the finishing forms, which deplete the gauge.

Background
Pandora's Box was a jar in Classical mythology which held all the evils of the world. It was given to the first woman, Pandora, as a gift for her wedding to Epimetheus, and she mistakenly opened it and released evil into the world.